Hydaulic power transmission system



Feb. 13, 1951 J. ROBINSON I 2,541,290

HYDRAULIC POWER TRANSMISSION SYSTEM Filed Aug. so, 1946 INVENTOR. JAM ES ROBINSON FITTDRNE'H Patented Feb. 13, 1951 mnauuc rowan SYSTEM TRANSMISSION James Robinson, Huntington Woods, Mich., as-

signcr to Vickers Incorporated, Detroit, Mich., a corporation of Michigan Application August 30, 1946, Serial No. 693,988

6 Claims.

This invention relates to power transmissions, particularly to those of the type comprising two or. more fluid pressure energy translating devices, one of which may function as a pump and another as a fluid motor.

This invention is particularly concerned with hydraulic transmissions having load characteristics requiring high torques at slow starting speed and lower torques at higher speeds. One of the inherent operating characteristics of hydraulic motors is that the torque output is inversely proportioned to the speed of rotation under constant power input. Due to the high torque starting requirement of certain load devices, the size of the hydraulic motor required to meet the demands may be impractical or uneconomicai to manufacture. At the same time, the high speed low torque range of the transmission can easily be met by a standard, small high speed motor.

Its is therefore the main object of this invention to employ the natural advantages of the small standard high speed low torque motor in a transmission in such a manner as to produce satisfactory high torque starting characteristics at lower speeds.

By gearing two or more motors to the load device, the sum of their torques can be used as a single force. By connecting the motors in parallel, the pump volume is divided between them thus decreasing their speed in proportion to the number of motors employed and increasing their combined low speed high torque delivery. If the same motors are connected in series, each receives the entire pump capacity resulting in high speed low torque characteristics as required under normal operating conditions in the case mentioned above.

Therefore, one of the objects of this invention is to provide means for connecting multiple motors in parallel during high torque starting speed and automatically shift the connections for series operation at normal operating speeds.

Another object is to provide means for automatically maintaining equal loads on all transmission motors connected in series.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred form of the present invention is clearly shown.

Inthe drawing:

The single figure is a diagrammatic view of a power transmission system incorporating a preferred form of the present invention.

The transmission includes a reverse flow variable delivery pump I0 driven by a prime mover I2 and connected by alternately pressure or return conduits I4 and I6 to hydraulic motors I8 and 20 which in turn are adapted to drive a load shaft 22 through motor pinions 24 and 26 and load shaft gear 28. Intermediate conduits 30 and 32 connect the motors Land 20 to ports 34 and 36, respectively, of a four-way valve 38. Pressure and return conduits I4 and I6 are connected to ports 42 and 40 of the fourway valve 38 by conduits 46 and 44, respectively. A double acting relief valve 48 is connected to conduits I4 and I6 across the pump ID by conduits 50 and 52. A pressure switch 54 is connected to the pressure and return conduits I4 and I6 by means of the conduit 56 provided with check valve 56 and 60. A pressure dividing valve 62 is connected to port 64 of the four-way valve 38 by conduit 66, to tank 68 by tank conduit 10 and to pressure conduit 56 by conduit 12.

A replenishing pump 14 is illustrated driven off the prime mover shaft I6 by a belt 18 and adapted to suck hydraulic fluid from tank 68 by conduit 66 and replenish the system through the conduit 82 and check valves 84 and 86 to conduits 50 and 52. A relief valve 86 in conduit 82 is connected to the tank conduit 10 by conduit 90. The double acting relief valve 48 comprises two pressure balanced piston control valves 92 and 94 in combination with check valves 96 and 98 for relieving excess pressure in either pres sure conduit I4 or l6 to the other conduit.

The pressure switch 54 comprises a ball resistance valve I00, piston I02, restricted by-pass I04 and discharge conduit I06. The push rod I08 is shown connected to a two-position switch IIO adapted to connect the solenoids H2 and H4 to a power source for shifting the four-way valve spool H6. The pressure dividing valve 62 includes a piston valve IIB provided with differential areas I20 and I22 and adapted to selectively connect conduit 66 to 12 by passage I26 and port I26, or to tank conduit I0 through chamber I28 and port I30.

In operation, pressure fluid is delivered by pump I0 to conduit I4. The transmission elements are illustrated in the drawing in their normal high speed or series operating position. The path of the pressure fluid in series operation is from pump III to conduit I4, first stage motor I8, conduits 30, ports 34 and 36 of the four-way valve 38, conduit 32, second stage motor 20, conduit I6, and return to the pump.

With the valve spool H6 in its series position as shown, port 04 is in communication with ports 24 and 38 and the intermediate conduits 20 and 32 are connected through conduit to the pressure dividing valve 82 and chamber I28. The differential piston area I20 of the twin motor circuit illustrated is approximately twice the size of the piston area I22. Theoretically, assuming two motors of equal displacement, the pump operating pressure of 2,000 pounds per square inch, the pressure in the intermediate conduits 30 and 22 in series operation should be approximately 1,000 pounds per square inch in order to impose equal loads on each motor. If the pressure in the intermediate conduit 30 and 22 rises above the 1,000 pounds per square inch, then the, force on piston area I20 will be greater than the force on area I22. The piston II8 will be shifted to open the chamber I28 to the tank port I30 thereby relieving the excess intermediate pressure through port 64 in the four-way valve 28 and conduit 66.

If the pressure in conduit 20 and 22 is below normal (1,000 p. s. 1.), the pump operating pressure (2,000 p. s. i.) will be admitted from conduit I4 through check valve 58, conduit I2 to chamber I23 and the smaller piston surface I22. If the pressure on the surface I20 is below normal (less than 1,000 p. s. 1.), the piston II8 willrise, uncover port I26 and by-pass the pump pressure fluid from chamber I20 through I22 through passage I24, conduit 66, ports 64, 24, and 36 into intermediate conduits 30 and 22.

Thus, the inlet pressure of the second stage motor will be raised to normal and equalize the load on the motor.

A transmission employing three motors in seequalize the load between the three motors of the same displacement, the pressure between the first and second stage would be two-thirds of the pump pressure and between the second and third stage, it would be one-third the pump pressure. The areas of the pressure dividing valve piston would be in the ratio of three to two for the first intermediate conduit and three to one for the second.

40 and conduit 44 directly to the pump conduit 1 I6. At the same time, motor 20, inlet conduit 22, and port 36 are connected by port 42 and conduit 46 directly to the pump conduit I4.

Thus, closing of the contacts I24 shifts the operation from series to parallel. In order to reverse the direction of rotation o shaft 22, the pump yoke is shifted by control wheel I36. Thus, conduits I4 and I6 may perform the function of either pressure or return conduits, respectively. All other elements of the transmission are designed and connectedv to 4 function uniformly regardless of the direction of flow or rotation.

It will thus be seen that the present invention has provided a transmission for producing high starting torques and lower operating torque at normal speed without sacrificing efficiency. This is accomplished by employing multiple hydraulic motors with novel controls adapted to automatically connect the motors in parallel 10 during low starting speed when the torque load is high, and automatically shift the connection to series and maintain equal loads on all motors during normal operation.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

l. A hydraulic power transmission employing multiple motors geared to a power take-off and connected to an operating pressure fluid supply, including a four-way valve adapted to connect the motors in parallel or series, andpressure actuated control means for selectively shifting the ploying a variable delivery, reversible flow pump connected to alternate pressure and return conduits, and multiple reversible motors geared to a load device comprising a four-way valve controlled by the operating pressure from the pump and adapted to connect the motors in series when the operating pressure is low, and in parallel at high operating pressures.

3. A control device for hydraulic transmissions employing a variable delivery, reversible flow 0 pump connected by conduits to multiple, reversible motors coupled to a load device and adapted for selective series or parallel operation including a four-way valve for connecting the conduits and motors in series when the pump pressure is low, and pressure controlled means for shifting the four-way valve and connecting the conduits and motors in parallel when the pump. pressure reaches a predetermined amount.

4. A control device for hydraulic transmissions When the torque loads are heavy as occur employing a variable delivery, reversible flow during the starting period, the pump pressure-,1 will increase until the four-way valve shifts and.

pump connected by conduits to multiple, reversible'motors coupled to a load device and adapted for selective seriesor parallel operation including a pressure dividing valve for maintaining a predetermined pressure in an intermediate conduit which connects consecutive motors when operating in series, including a differential piston valve controlled by the differential pressure between the intermediate conduit and the pump delivery conduit. whereby excess pressure in the intermediate conduit will be ported to tank, and pump delivery pressure will be admitted to the inter- :ne d iate conduit when its operating pressure is below normal.

5 5. A control device for hydraulic transmissions jemploying a variable delivery, reversible flow pumpconnected by conduits to multiple, reversible motors coupled to a load device and adapted for selective series or parallel operation including 761a four-way valve for connecting the conduits and motors in series when the pump pressure is low, and pressure controlled means for shifting the four-way valve and connecting the conduits and motors in parallel when the pump pressure reaches a predetermined amount, and a relief 2,541,290 5 6 valve connected to the pressure and return con- REFERENCES CITED duits in parallel with the pump and adapted to relieve excess pressure in one conduit by exhaust- The following references are of record in the ing into the other. me of this patent 6. A control device for hydraulic transmissions 5 UNITED STATES PATENTS employing a variable delivery, reversible flow Number Name Date pump connected by conduits to multiple reversti; 2,079,263 wiedmann May 4, 193-7 ble motors of equal displacement and coupled a load device and adapted for selective series or FOREIGN PATENTS parallel operation including a four-way valve for 10 Number 1 Country Date connecting the conduits and motors in series 184,455 Great Britain Oct. 18, 1923 when the pump pressure is low, and pressure controlled means for shifting the four-way valve and connecting the conduits and motors in parallel when the pump pressure reaches a pre-determined l5 amount.

JAMES ROBINSON. 

